The present invention relates to a mass spectrometer and a method of mass spectrometry.
Orthogonal acceleration Time of Flight mass spectrometry has proved to be an invaluable tool in many applications. Historically, the benefits of orthogonal acceleration Time of Flight mass spectrometry include high resolution, good mass measurement accuracy and excellent full mass range sensitivity.
In most known orthogonal acceleration Time of Flight mass analysers the period between extraction pulses is arranged to be greater than or equal to the time of flight of ions having the maximum mass to charge ratio within the mass spectrum. So, for example, if a first extraction pulse is produced at a time T1, wherein ions having the lowest mass to charge ratio have a time of flight ΔT1min through the time of flight region and ions having the highest mass to charge ratio have a time of flight ΔT1max through the time of flight region and wherein a second extraction pulse is applied to the acceleration electrode at a subsequent second time T2, then T2−T1≧ΔT1max.
The fast experimental times associated with conventional orthogonal acceleration Time of Flight mass spectrometers make orthogonal acceleration Time of Flight mass spectrometer an ideal choice for tandem instruments such as ion mobility-Time of Flight mass analysers (IMS-ToF) and ion trap-Time of Flight mass analysers (IT-ToF). According to such arrangements the separation afforded by the IMS device or the ion trap can be profiled by the orthogonal acceleration Time of Flight analysers without significant sensitivity losses.
WO2008/087389 discloses a Time of Flight mass analyser wherein the time period between successive orthogonal acceleration pulses is less than the time of flight of ions having the maximum mass to charge ratio of interest. Some ions are subject to wrap-around and will appear in a subsequent mass spectrum. Mass spectra are obtained at two different sampling rates and are compared. Mass peaks relating to ions which have been subject to wrap-around are identified. So, for example, if a first extraction pulse is produced at a time T1, wherein ions having the lowest mass to charge ratio have a time of flight ΔT1min through the time of flight region and ions having the highest mass to charge ratio have a time of flight ΔT1max through the time of flight region and wherein a second extraction pulse is applied to the acceleration electrode at a subsequent second time T2, then ΔT1max−ΔT1min>T2−T1<ΔT1max. As a result, some mass spectral data relating to two subsequent orthogonal acceleration pulses will overlap. Mass spectral data which is subject to wrap around is then identified and corrected.
It is desired to provide an improved Time of Flight mass analyser and method of mass analysis.